Space vehicles such as artificial satellites and other payloads, which shall be designated in the entire present description by the term “satellites”, are intended to be stationed in orbit around a celestial body, in particular in Earth orbit, more particularly in geostationary orbit, in order to successfully carry out their mission, for example telecommunications, observation, and so forth. This stationing is usually carried out in two steps. The first step consists in launching the satellite into space, especially from the Earth's surface, by means of a vehicle specifically dedicated to this, commonly known as a launch vehicle, and injecting it into an initial orbit, known as the injection orbit. In the second step, the satellite is transferred from this injection orbit to its mission orbit, also known as the final orbit. Satellites are classically equipped with a propulsion system able to maintain them in the mission orbit, and then, if appropriate, at the end of their life, to transfer them into their graveyard orbit.
The transfer of the satellite from the initial orbit to the mission orbit for its part can also be accomplished by the satellite's own propulsion means. For this, the satellites may be equipped with propulsion systems comprising a chemical propulsion module with greater thrust to accomplish the transfer from the injection orbit to the mission orbit, and a chemical or electrical propulsion module of lower thrust for the orbital maintenance maneuvers.
In the most common instances, the injection orbit is a geostationary transfer orbit (GTO) and the satellite is transferred into geostationary orbit by one or more firings at the apogee of this GTO orbit by a dedicated chemical thruster.
Recently, electrical propulsion has also been used to accomplish such a transfer. This makes it possible to achieve better performance as compared to chemical propulsion. However, the lower thrust of the electrical propulsion results in longer transfer times. For the transfer phase, this therefore requires the satellite to be equipped with substantial thrust capabilities, which lead to major constraints on the dimensioning of the electrical propulsion system and the power system in order to obtain reasonable transfer times, that is, of the order of several months. These constraints have an unfavorable impact on the weight and the cost of the satellite.
It has otherwise been proposed by the prior art to implement, for the transfer of the satellite from its injection orbit to its mission orbit, an independent spacecraft able to dock to the satellite in the injection orbit and provided with means of propulsion making possible an orbit transfer. Such a spacecraft, described in particular in the document US 2005/0151022, is furthermore equipped with means enabling refilling of its tank with propellant, in orbit, from a service vehicle which has been positioned in said orbit for this purpose. However, the implementation of such a spacecraft is costly and onerous, especially because its resupply with propellant requires several steps which are complicated and time-consuming to accomplish.